Invasion, plain and simple.
There was a time in Western Europe's history when they fought back, overcame, and then expelled the muslims from their lands.
Not -some- of the muslims, but ALL of them.
Unfortunately, this time they have neither the wisdom nor the intestinal fortitude required to repeat what is historically required for their own survival.
Today's election in France is exhibit A.
The Western Europeans will wake up someday and realize the enormity of the enemy within that they face, but in all likelihood it will then have become too late...